VCCA Home Forums TECHNICAL - GENERAL Commercial Vehicles COE 41-42 BB Carb Problem No. 489S

Help! I have a 489S updraft carb that is filling the inlet side with fuel. I have it connected to a vaccum tank, a 6-volt momentary fuel pump to refill the tank and the main fuel tank.
I have verified the orifices are clear, all check valves were checked or replaced, the carb pump is working and initially, at startup, the carb works supplying fuel to the engine. After running for a minute or two the, the inlet side begins to fill up to the point that the choke butterfly, when pulled, sweeps fuel out of the air inlet. I also replaced the inlet valve on the float. Does anyone know what the problem may be. I'm a Chevy guy who just couldn't pass up a 1923 Buick rebodied with a Cantrell body in 1929. This vehicle has ran fine with the above carb since being restored in 1984. It has been in storage for five years-hence the current problem. Thanks.

I don't understand from your description what is the problem. Is the carb running out of fuel? Too much fuel? Is the vacuum pump used to deliver fuel to the carb by itself or is the electric pump used to fill the tank periodically. Or is the electric pump only used when the vacuum tank runs low? Is the electic pump used to supply the carburetor directly and the vacuum tank only have a pipe going through it? Why do you use the choke butterfly when the engine has been running for a minute or two?

If overfueling is the problem then the float/needle are not properly limiting the fuel flow. It can be trash in the fuel, bad valve, too high pressure for needle/seat, gum or varnish on the needle/seat or similar problem.

Chipper, could a constant running electric pump overfill the vacuum pump tank and cause gas to run back down into the intake thru the vacuum line then down and out the carb air inlet?

MrMack,

The electric pump is only used(momentary) to prime the vacuum tank after long periods of inactivity. Meaning, it only runs when a switch is held in, once released, it shuts off.

Thanks,

Chief

Chipper,

The needle valve(seat and needle) for the float was changed to a new one. It was tested by holding the float up lightly and blowing into the inlet to it. The carb was cleaned extensively, every orifice, ball checks and carb cleaner sprayed into and out of every orifice and passage way. Then air was blown thru each to verify they were open.

There is way too much fuel, as the air inlet gets so full the fuel can be swept out by applying the choke-which was done to try to keep it running as it began to stall after initially running smooth for a minute or so. I am asking what may be causing this excess fuel to appear in the inlet. Is it one particular valve(check), possibly a leaking body gasket, or what?
The main tank was drained of what little yellowed fuel that was left in it. The drained fuel was clean, there does not appear to be any trash in the tank(we can visually see into the bottom of the tank and it is clear and clean.

The previous owner had tried to start it, with no success, except starter fluid. Initially, we could only start it on starter fluid. So, we cleaned the carb, inspecting everything and changed parts with good used or new, as we found some bad parts. Now, we have fuel and it will run for 1-5 minutes before it floods(?) and falters. We have retimed it and verified we have spark(changed plugs and condensors.

As previously stated, this settup worked perfectly for 20 years.
I can change out the needle and seat again, as I have others(new). As I indicate in my reply to MrMack, the pump only charges the vac. tank after long periods of inactivity. The vac tank appears to work fine and was rebuilt several years ago by a local tank specialist, Ben Hodgekiss, now deceased.

Thanks,

Cheif

Chief
you might try change the following needle valve and seat and gasket, plus float. sounds to me like the float is sticking open for some reason,causing it to flood

I agree that the problem is in the float, needle/seat. Is the seat gasket cracked, housing where the seat gasket seals rough or seat loose? Is the float cracked? Leaking? Have liquid in it? There are only three parts that control overfilling of the float bowl and then out of the intake passage (float, needle, seat). The problem has to be one or more of them. That is with the fractional pound fuel pressure from gravity flow of the vacuum tank.

It is very common for original and even new needle/seat/float combinations to leak when 2-7 psig fuel pressure from an electric pump. In this case the electric pump is not the problem as it is only used to fill the vacuum tank after extended idle periods. I use similar setup on several of my vehicles, particularily those that are used as test engines verifying correct carb rebuilds.

If the carb causes the engine to run rich then there are several other possible causes. Jet sizes, oversize low-speed jet passage are among them.

i would eliminate the vacuum tank by running the engine on a temp. tank we use a old lawn mower tank plug the vacuum line at the tank or manifold and try if this fixes the problem you need to work on the vacuum tank if not the carb

Check that the floats do actually float. If they dont they wont close the needle and seat and cause flooding.
Tony

Thanks for all the input. I did verify the float actually floats. I was limited to the main jet(only one available), etc.

I gave up on the carb and installed the original Marvel carb and with the help of an octogenian, we got it running. I am now looking for a spring for the air valve, on the Marvel carb.

Thanks again,

Chief